Nested spring assemblies are commonly used in a variety of applications. Such assemblies generally comprise two springs, one having a larger diameter than the other. The spring having the smaller of the two diameters may be placed within a cavity formed by the spring having the larger of the two diameters.
When the inner diameter of the larger spring is only slightly larger than the outer diameter of the smaller spring, the smaller spring is typically nested tightly within the larger spring, due to an interference-type fit between the two springs.
There are instances, however, when the inner diameter of the larger spring is somewhat larger than the outer diameter of the smaller spring. Under these conditions, the smaller spring may move within the cavity formed by the larger spring.
Moreover, when there is an even larger disparity between the outer diameter of the smaller spring and the inner diameter of the larger spring, there is an increased risk that the smaller spring may become separated from, i.e., fall out of the cavity formed by, the larger spring. This separation may occur during transport of the nested spring assembly from its manufacturer to the ultimate user, or during placement of the nested spring assembly into the device in which it is ultimately intended to be used, such as an automotive automatic transmission, a manual clutch disc, a hydraulic pump, an engine valve train, and various other similar applications.
Such separation is obviously problematic. If the separation occurs during transport, then loss of the second spring can occur, rendering the spring assembly useless for its intended purpose. If the separation of the smaller and larger springs occurs prior to placement into the device in which it is ultimately intended to be used, then manufacturing of the device is at least delayed.
To avoid these problems, and especially the potential for separation, current two-spring assemblies are wrapped in cellophane or other similar wrapping, or are placed in trays or magazines for transport and preparation for assembly. Such wrapping must be removed prior to placement of the nested spring assembly into the automatic transmission or other device, or the springs must be removed from the tray or magazine, slowing and adding to the expense of the manufacture of the automatic transmission or other device. During their removal from the trays or magazines, the springs can be inadvertently separated, and one or both of the two springs could fall to the ground, further slowing the assembly process.
Other prior art known to the Applicant does not effectively solve these problems. For example, U.S. Pat. No. 4,148,469 issued to Geyer on Apr. 10, 1979, and is assigned to Standard Car Truck Company. This patent discloses a dual rate spring system having a primary and secondary spring forming a spring unit. The claims disclose a primary spring that is longer than the secondary spring (Claim 1, Column 3, lines 12-13). The bottom coils of the springs are seated upon a side frame spring seat surface, and are bonded together or encased within a rubber or elastomeric material (Claim 1, Column 3, lines 14-15). This bonding agent provides a yielding, but positive, connection between the lower coils of the two springs (Column 2, lines 28-30). The springs appear to be bonded together by an elastomeric material at their coterminating lower ends. Moreover, the bonding agent provides a permanent connection of the two springs and is not intended to break or dissolve when in use.
U.S. Pat. No. 5,203,546 issued to Amadore on Apr. 20, 1993. This patent discloses a window spring damping apparatus having a coiled spring member slipped over a balance spring which is encased within the bore of a rigid tubular spring cover. The coiled spring member has a varying diameter to engage the bore of the spring cover (Claim 1, Column 3, lines 30-36; and Claim 5, Column 4, lines 24-32). The coiled spring member 10 has a positioning section 22 which has a diameter corresponding to the diameter of the balance spring 12 such that when the coiled spring member is slipped over the balance spring, the turns of the balance spring are retained between the turns of the position section (FIG. 1; and Column 4, lines 1-9). Thus, the coiled spring member is in a relatively fixed position along the length of the balance spring, keeping the balance spring firmly positioned away from the walls of the spring cover 14 (FIG. 1; and Column 4, lines 6-8). This patent teaches a positioning of the two springs to prevent movement. In addition, the claims require a spring cover on either side of the coiled spring member to prevent movement.
U.S. Pat. No. 4,718,868 issued to Williams on Jan. 12, 1988. This patent discloses an annular coiled spring. The annular coiled spring comprises a first coiled metallic spring coupled together by a second coiled metallic spring forming an annular configuration (FIG. 4; and Column 1, lines 48-50). This configuration facilitates electrical contact (Column 2, lines 1-2). The annular coiled spring is adapted to fit around a cylindrical member of an apparatus for electrically connecting together the inner and outer contacts (Column 1, lines 18-22).
U.S. Pat. No. 4,282,979 issued to Friedrichs on Aug. 11, 1981. This patent discloses a force absorbing arrangement having a friction spring, and a device for immediate buffer coupling of rail vehicles, including an elongated housing with one closed end.
U.S. Pat. No. 3,511,280 issued to Mercier on May 12, 1970. This patent discloses a pressure vessel having two coaxial helical springs. The two coaxial helical springs are positioned to provide equal torque effects in opposite directions (Column 6, lines 14-31).
U.S. Pat. No. 3,556,504 issued to Sinclair on Jan. 19, 1971. This patent discloses suspension systems having a spring unit. The spring unit provides different spring rates for a vehicle suspension system in tare and gross load positions, and comprises an inner and outer spring disposed coaxially, one within the other (Column 3, lines 14-15). The spring unit acts in series in the tare condition and in parallel in the gross condition (Column 3, lines 23-25). The inner and outer springs form a spring abutment defining the extension of the two springs, and are separated by an inner telescopic member 24 (Column 3, lines 18-19).
U.S. Pat. No. 4,907,788 issued to Balsells on Mar. 13, 1990. This patent discloses a dual concentric canted-coil spring apparatus. The apparatus has a first annular spring and a second annular spring disposed within the first annular spring. FIG. 15 illustrates the annular coil spring apparatus 400, including a first annular spring 402 having a second annular spring 404 disposed therein in an axial relationship. As can be seen most clearly in FIG. 7b, each spring has a front angle 116 which is greater than the back angle 112. The coils are traced in a circular-like manner about the center line 104.
U.S. Pat. No. 4,186,914 issued to Radwill et al. on Feb. 5, 1980. This patent discloses a dual rate spring device for railroad cars. The dual rate spring comprises a light duty spring disposed within a heavy duty spring (Claim 1, Column 5, lines 45-49; and Claim 4, Column 6, lines 43-44). A spring retainer element 34 (FIG. 1) is loosely positioned between the inner receiving space of the heavy duty spring and the bottom coil convolution of the heavy duty spring to inhibit movement of the spring (Claim 1, Column 2, line 44). The light duty spring has one end disposed within the heavy duty spring and contacts the spring retaining element (Claim 1, Column 4, lines 45-46). The spring retaining element has a lateral slot and is disposed within the inner space of the heavy duty spring (Claim 4, Column 6, lines 37-38). The light duty spring is disposed within the inner space of the heavy duty spring and is in contact with the bottom coil convolution of the heavy duty spring.